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suppressPackageStartupMessages(library("modelr"))

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1. Use geom_text() with infinite positions to place text at the four corners of the plot.

I can use similar code as the example in the text. However, I need to use vjust and hjust in order for the text to appear in the plot, and these need to be different for each corner. But, geom_text() takes hjust and vjust as aesthetics, I can add them to the data and mappings, and use a single geom_text() call instead of four different geom_text() calls with four different data arguments, and four different values of hjust and vjust arguments.

label <- tribble(
  ~displ, ~hwy, ~label, ~vjust, ~hjust,
  Inf, Inf, "Top right", "top", "right",
  Inf, -Inf, "Bottom right", "bottom", "right",
  -Inf, Inf, "Top left", "top", "left",
  -Inf, -Inf, "Bottom left", "bottom", "left"
)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_text(aes(label = label, vjust = vjust, hjust = hjust), data = label)

2. Read the documentation for annotate(). How can you use it to add a text label to a plot without having to create a tibble?

With annotate you use what would be aesthetic mappings directly as arguments:

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  annotate("text",
    x = Inf, y = Inf,
    label = "Increasing engine size is \nrelated to decreasing fuel economy.", vjust = "top", hjust = "right"
  )

3. How do labels with geom_text() interact with faceting? How can you add a label to a single facet? How can you put a different label in each facet? (Hint: think about the underlying data.)

If the facet variable is not specified, the text is drawn in all facets.

label <- tibble(
  displ = Inf,
  hwy = Inf,
  label = "Increasing engine size is \nrelated to decreasing fuel economy."
)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_text(aes(label = label),
    data = label, vjust = "top", hjust = "right",
    size = 2
  ) +
  facet_wrap(~class)

To draw the label in only one facet, add a column to the label data frame with the value of the faceting variable(s) in which to draw it.

label <- tibble(
  displ = Inf,
  hwy = Inf,
  class = "2seater",
  label = "Increasing engine size is \nrelated to decreasing fuel economy."
)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_text(aes(label = label),
    data = label, vjust = "top", hjust = "right",
    size = 2
  ) +
  facet_wrap(~class)

To draw labels in different plots, simply have the facetting variable(s):

label <- tibble(
  displ = Inf,
  hwy = Inf,
  class = unique(mpg$class),
  label = str_c("Label for ", class)
)

ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
  geom_text(aes(label = label),
    data = label, vjust = "top", hjust = "right",
    size = 3
  ) +
  facet_wrap(~class)

4. What arguments to geom_label() control the appearance of the background box?

• label.padding: padding around label
• label.r: amount of rounding in the corners
• label.size: size of label border

5. What are the four arguments to arrow()? How do they work? Create a series of plots that demonstrate the most important options.

The four arguments are (from the help for arrow()):

• angle: angle of arrow head
• length: length of the arrow head
• ends: ends of the line to draw arrow head
• type: “open” or “close”: whether the arrow head is a closed or open triangle